Lead is a ubiquitous and harmful environmental pollutant. The EPA has established the action level for lead at 72 nM. In certain nonaqueous solvents in the presence of high bromide concentrations (tetrabutylanimonium bromide), lead clusters (Pb4Br11)3− form. These clusters have a moderately efficient luminescence (greenish) that has been proposed as an analytical tool for detecting lead. However, the method is inadequate for direct use with environmental samples because it only works in nonaqueous media and fails in the presence of a small amount of water. This problem would necessitate complex and time consuming pretreatment of samples.
Lead is a toxic metal which can be harmful to human health even at low exposure levels. Lead is sometimes referred to as a cumulative toxin because the lead concentrates in the body. Young children, infants, and fetuses are particularly vulnerable to lead because the physical and behavioral effects of lead occur at lower exposure levels in children than in adults. Overexposure to lead can permanently impair a child's mental and physical development. Comparatively low levels of exposure have been linked to damage to the central and peripheral nervous system, learning disabilities, shorter stature, impaired hearing, and impaired formation and function of blood cells. At its worst, lead poisoning can result in stupor, coma, kidney damage, or severe brain damage.
Lead in drinking water (i.e., potable water) can be a significant contributor to overall exposure to lead, particularly for infants whose diet consists of liquids made with water, such as baby food formula. Consequently, there is a great need to test potable water to determine whether such water contains less than the five parts per billion (ppb) maximum limit proposed by the EPA for public drinking water and to check for less than 10 parts per billion on first draw samples at the point of use. One ppb is equal to one microgram per liter.
Although it is possible to analyze water samples using atomic absorption (i.e. spectroscopic analysis) techniques, such techniques are cumbersome and subject to error due to interferences. For example, the sample must first be prepared in order to convert organic forms of lead to inorganic forms, to minimize organic interferences, and to convert the sample to a suitable solution for analysis. Then the prepared sample is placed into a graphite tube furnace where the sample is slowly evaporated to dryness, charred (ashed) and then atomized. The absorption of hollow cathode radiation during atomization is proportional to the lead concentration.
The atomic absorption method is subject to various disadvantages. For example, it requires the use of an atomic absorption spectrophotometer and a graphite furnace. It also requires a trained operator, a lengthy set-up time, and the equipment required is extremely expensive. Thus, this technique is not suitable for use in the field. Rather it must be used in the laboratory.
Also, the atomic absorption method is subject to various types of interference. The long residence time and high concentrations of the atomized sample in the optical path of the graphite furnace can result in severe physical and chemical interferences. Furnace parameters must be optimized to minimize such effects. Lead analysis can also suffer from severe nonspecific absorption and light scattering caused by matrix components during atomization. Simultaneous background correction must be employed to avoid erroneously high results. Also, if the analyte is not completely volatilized and removed from the furnace during atomization, memory effects will occur, thereby requiring cleaning of the tube by operating the furnace at higher atomization temperatures. Further, the presence of sulfate can suppress lead absorbance, thereby requiring the use of a lanthanum-releasing agent.
There is a long felt need in the art for rapid, simple detection of lead in samples such as drinking water, plant, and water treatment effluent, hazard waste sites, streams, estuaries and coastal waters. The present invention satisfies this need.